It is well known from the prior art to provide speed cameras which instantaneously detect the speed of a vehicle and take a photograph of it and if the vehicle is speeding at the moment when the photograph is taken then a penalty is issued. However, these cameras have the disadvantage that when their location is known then motorists will slow down as they approach the cameras in order to come under the speed limit, but may exceed the speed limit between cameras with no detection possible.
On toll roads it has been proposed in the past that the time taken for a vehicle to travel between tolls can be measured and then an average speed calculated from the time between tolls and the distance between the tolls. If this average speed is above the speed limit then a penalty can be issued. However, this solution requires the construction of tolls and the associated costs related to such tolls and the inconvenience to motorists of having to pass through toll gates.